Undoubtedly, reflection posts have substantial advantages as optical guiding means when driving in the dark on a road. Such posts are commonly used in most countries.
The inventor of the present invention has made an investigation of optical guiding system for roads. The investigation was made as a report for achieving a Degree in Management at the University of Gothenburg and led to a number of results, of which the following are the most important:
1. Reflection posts are efficient and economically justified optical road guiding instruments.
2. No matter which direction the driver drives his vehicle, it should be possible for him to utilize the reflection posts at both road margins. These except being able to see the reflection elements at the side of the road used by the driver, it should also be possible for him to see the reflection elements at the other side of the road. Therefore, there should be reflecting surfaces at both sides of reflection posts of this kind.
3. The reflection ability is improved if the continuous reflection area of the reflection device is increased. For optimizing the utilization of available space, circular form of the reflection surfaces is preferably used (the minimum area of a reflection surface should be at least 12.5 cm.sup.2).
4. On "common roads", the spacing between the reflection devices or posts should be approximately 33 m, and on expressways the distance between posts should be approximately 50 m. The distance from the road border should be approximately 0.5 m.
5. Due to the climate in many countries, the reflection elements are adversely affected by dirt or soiling. Dirt decreases the reflection ability, and the necessary cleaning implies costs.
6. However, the investigation discloses that considerable saving of costs can be obtained if the reflection elements are detachable from the reflection devices or reflection posts, so that the reflection elements can be cleaned separately.
Thus, there is a need for a reflection device or reflection post giving reflection effect in both driving directions, preventing or substantially preventing or delaying soiling of the reflection surfaces and being so arranged that it is detachable from the reflection device or reflection post for making possible a cleaning if necessary.